The long term goal of this project is to understand the regulation and physiological roles of autophagy, a process by which proteins, organelles and bulk cytoplasm are sequestered within autophagic vesicles and delivered to the lysosome for degradation. This process plays several distinct, vital roles in the cell, acting to recycle aged or damaged components, to provide a source of nutrients in response to starvation, and in some cases to initiate cell death. These cellular functions underlie the impact of autophagy on a broad range of human illnesses. Fundamental questions regarding autophagy remain to be addressed, including how autophagy is regulated by nutrients and other signals, how substrates are selectively targeted for degradation, and how autophagy can promote either cell survival or cell death in different contexts. The proposed studies will use genetic, biochemical and imaging-based approaches in the Drosophila system to help define mechanisms of autophagy regulation and its functions in an intact organism. Recent studies in Drosophila and mammalian cells have delineated key factors in a conserved signaling pathway that inhibits autophagy under favorable nutrient conditions. The central component of this nutrient-sensing pathway, the Ser/Thr protein kinase Target of Rapamycin (TOR), was shown to control the activity of a multicomponent complex containing the autophagy related kinase Atg1 and the phosphoprotein Atg13. Specific aims of this project are to: 1) test potential models of Atg1/13 complex regulation, including the effects of phosphorylation, multimerization, and association with novel inhibitory cofactors. Potential roles of PKA in this regulation as well as the function of the Atg1-related kinase Ulk3 will be characterized. 2) investigate mechanisms and consequences of a novel self-reinforcing feedback signal by which Atg1 inhibits TOR signaling. 3) investigate mechanisms by which Atg1 overexpression leads to autophagy-dependent cell death. As preliminary indicate of a role for Jun kinase (Jnk) signaling, the mechanisms of autophagy induction by Jnk and the roles of autophagy in endogenous Jnk-mediated death will be explored. 4) identify and characterize the functions of novel autophagy regulators and substrates through genetic and proteomic screens. Experiments in these aims were selected for their likelihood of having a high impact on key questions important to the field of autophagy. This proposal makes use of recently developed reagents including knockouts of several autophagy-related (Atg) genes, in vivo markers of autophagic activity, and novel methods of genetic manipulation. Information gained from studies of autophagy in Drosophila will provide an important whole- animal complement to mammalian cell culture-based studies.